I agree with @Ragnia that it was Alice's mother. However, my guess is that the Witch would have made herself immune to the curse, and I'm betting that Alice is immune, too. The end result will be that Alice and the Duke could have been having sweet sexy times this whole time
Yeah, it's probably going to be Alice's mom that cursed him and Alice will either be immune OR touching her will break the curse. Now, why she would curse him in the first place is still a mystery, because from the way people have talked about her, she didn't seem be to evil.
So he'd be able to be with Alice. Alice has loved him since she was a kid and the only reason I'd guess her mom would curse him was so he wouldn't marry some other noble his family picked. Since normally there's no way he'd be able to marry Alice (a maid). And yeah I've always expected Alice to be immune to the curse because it was done for her sake.